Process for the production of crystalline sodium sheet silicate with kanemite structure

ABSTRACT

The present invention relates to a process for the production of crystalline sodium sheet silicate with kanemite structure with the chemical formula 
     
         NaH Si.sub.2 O.sub.5 ·X H.sub.2 O 
    
     in which X represents a value between 1 and 3. Crystalline sodium sheet silicate with kanemite structure is produced by maintaining a mixture of sodium disilicate, silica and water in the molar ratio of 1:2:(6-8) at a temperature of 20° to 100° C. for a period of 0.2 to 10 h.

The present invention relates to a process for the production ofcrystalline sodium sheet silicate with kanemite structure with thechemical formula NaH Si₂ O₅ ·X H₂ O in which X represents a valuebetween 1 and 3.

Modern light-duty detergents and dishwashing agents should have a low pHof 8 to 10 and represent mixtures of many substances containing, interalia, builders, cobuilders, a bleaching system and a stabilizer.Moreover, sodium tripolyphosphate or zeolite A, for example, are used asbuilders, polycarboxylates are used as cobuilders, percarbonate or amixture of perborates and tetraacetylethylenediamine (TAED) is used asbleaching systems, and phosphonates are used as stabilizers.

EP-C 164 514 discloses a detergent and cleaner which, besidessurfactants, contains crystalline sodium silicates in sheet form withthe composition NaMSi_(x) O_(2x+1) ·yH₂ O (with M equal to sodium orhydrogen, x from 1.9 to 4 and y from 0 to 20) as builders. Moreover,crystalline sodium silicates show a higher calcium binding capacity thanamorphous types, which is attributable to their structure in sheet formwith increased degree of polymerization.

Known crystalline sodium silicates occur in nature, but they are alsoproduced artificially, for example

    ______________________________________                                        Natrosilite        Na.sub.2 Si.sub.2 O.sub.5                                  Kanemite           NaHSi.sub.2 O.sub.5.3H.sub.2 O                             Makatite           Na.sub.2 Si.sub.4 O.sub.9.3H.sub.2 O                       Magadiite          Na.sub.2 Si.sub.14 O.sub.29.11H.sub.2 O                    Kenyaite           Na.sub.2 Si.sub.22 O.sub.45.10H.sub.2 O                    ______________________________________                                    

Of particular interest for use in light-duty detergents and dishwashingagents are the sodium silicates derived from the structure of kanemite,because these display in the wash liquor a lower pH than the sodiumsilicate which is mentioned in EP-C 164 514 and is essentially composedof δ-Na₂ Si₂ O₅. Kanemite can be produced by treating either β-Na₂ Si₂O₅ or α-Na₂ Si₂ O₅ with a water/methanol mixture at 100° C. withsubsequent heating at 700° C. for 5 to 24 hours and final extraction ofthe heated material with water.

The disadvantage in this case is that this production is elaboratebecause of the need for controlled addition of the individual substancesand requires considerable safety precautions because of the flammabilityof methanol.

Kanemite can be obtained by a variant described in EP-C 164 514 whenδ-Na₂ Si₂ O₅ is hydrolyzed with water, and the solid is filtered off anddried at 40°-105° C.

The disadvantages of this variant are that the hydrolysis results in asolid which is difficult to filter, and one equivalent of NaOH isremoved with the filtrate.

The object of the present invention is to indicate a process for theproduction of crystalline sodium sheet silicate with kanemite structureof the chemical formula NaHSi₂ O₅ ·XH₂ O in which X represents a valuebetween 1 and 3, with a high Ca binding capacity of 60 to 100 mg Ca/g(based on NaHSi₂ O₅) and a pH of 10 to 11 for a suspension of 1 g/1000ml of water, which operates without filtration and where the sodium ionsintroduced into the process remain in the crystalline sodium sheetsilicate with kanemite structure.

The object is surprisingly achieved by sodium disilicate, silica andwater being mixed in the molar ratio of 1:2:(6-8) and maintained at atemperature of 20° to 100° C. for a period of 0.2 to 10 h.

Furthermore, optional embodiments of the process according to theinvention can entail

a) employing as sodium disilicate δ-Na₂ Si₂ O₅ or a mixture of δ-Na₂ Si₂O₅ and up to 80% by weight of amorphous Na₂ Si₂ O₅ ·n H₂ O;

b) employing as silica precipitated silica, pyrogenic silica, silica solor silica gel;

c) employing the sodium disilicate with a particle fineness of less than1000 μm;

d) employing the silica with a particle fineness of less than 200 μm;

e) maintaining the reaction product where appropriate at 50° to 100° C.for a further 0.5 to 5 h;

f) comminuting the crystalline sodium sheet silicate with kanemitestructure by milling to a particle fineness of less than 100 μm.

The crystalline sodium sheet silicate with kanemite structure producedaccording to the invention can be used as detergent and cleaner builderto eliminate the hardness of water which contains calcium and/ormagnesium ions.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an X-ray diffraction diagram of the product of the presentinvention.

FIG. 2 is an X-ray diffraction diagram of a product made by acomparative example.

The crystalline sodium sheet silicate with kanemite structure producedaccording to the invention can be composed of

NaHSi₂ O₅ ·1H₂ O or

NaHSi₂ O₅ ·3H₂ O.

Since the partial pressure of water vapor from NaHSi₂ O₅ ·3H₂ O is higheven at temperatures of 40°-70° C., it is possible to convert part ofthe NaHSi₂ O₅ ·3H₂ O into NaHSi₂ O₅ ·1H₂ O. The value for X thusrepresents a value which indicates what proportion of the NaHSi₂ O₅ ·3H₂O is already in the form of NaHSi₂ O₅ ·1H₂ O.

If it is particularly important that the crystalline sodium sheetsilicate with kanemite structure according to the invention acts toeliminate the hardness of water, a good crystallinity is desirable. Thecrystallinity of the sodium sheet silicate with kanemite structure canbe increased further by a subsequent thermal treatment.

It may be regarded as surprising that, under the production conditionsaccording to the invention, crystalline sodium sheet silicate withkanemite structure is formed even if up to 80% by weight of thecrystalline δ-sodium disilicate are replaced by amorphous sodiumdisilicate in the reaction mixture. Reaction of quartz powder and δ-Na₂Si₂ O₅ astonishingly does not lead to the formation of crystallinesodium sheet silicate with kanemite structure.

LIST OF STARTING SUBSTANCES

1. δ-Na₂ Si₂ O₅ : Was produced by the procedure of DE-A 41 42 711 andcan be purchased as SKS-6 from Hoechst AG, Frankfurt.

2. Na₂ Si₂ O₅ (18% H₂ O): Amorphous sodium disilicate was purchased fromSociete Francaise Hoechst, Paris.

3. Precipitated silica: Type FK 320 was purchased from Degussa AG,Hanau.

4. Silica: Type HDKP 170 was purchased from Wacker-Chemie GmbH, Munich.

5. Silica sol: Type Klebosol 1346 was purchased from Societe FrancaiseHoechst, Paris.

6. Quartz powder: Type Microsil 20 was purchased from F. Lieben,Maastricht.

EXAMPLE 1

The following were mixed in a Type KM 70 D mixer from Lodige, Paderborn,

3643 g of δ-Na₂ Si₂ O₅ (SKS-6)

2451 g of precipitated silica, loss on drying at 105° C. 6% by weight;loss on ignition at 1000° C. 5% by weight; particle size 0.2% byweight>45 μm; SiO₂ content: 98% by weight

and

2522 g of water.

The solid mixture was then maintained at a temperature of 60° C. in aclosed container for 8 h. After cooling, the product was broken up andmilled.

Screen analysis of the final product was as follows:

10%<6.7 μm

50%<28.3 μm

90%<66.5 μm

Lines of δ-Na₂ Si₂ O₅ are no longer identifiable in the X-raydiffraction diagram of this product. Only kanemite lines are observed(FIG. 1). The pH of the substance is 10.9 (1 g/l; 7 min), the calciumbinding capacity is 75 mg Ca/g (based on NaHSi₂ O₅).

EXAMPLE 2

The following were vigorously mixed in a laboratory mortar

129 g of silica, SiO₂ content: 98% by weight loss on drying: 6% byweight,

182 g of δ-Na₂ Si₂ O₅

with

130 g of water

and then maintained at 60° C. in a closed glass bottle for 2 h. Aftercooling, the product was milled.

The X-ray diffraction diagram showed only kanemite lines.

EXAMPLE 3

The following were mixed together in a laboratory mortar

400 g of silica sol, SiO₂ content: 30% by weight,

100 g of δ-Na₂ Si₂ O₅

and

100 g of amorphous sodium disilicate.

172 g of water were evaporated out of this mixture at 60° C. Theremaining mixture was maintained at 60° C. in a closed bottle for 2 hand, after cooling, ground in a mortar.

The X-ray diffraction diagram showed only kanemite lines.

COMPARATIVE EXAMPLE

The following were vigorously mixed in a laboratory mortar

120 g of quartz powder, SiO₂ content: 99.3% by wt. d₅₀ 4.4 μm,

180 g of δ-Na₂ Si₂ O₅

and

130 g of water

and subsequently maintained at 60° C., in a closed bottle for 8 h. Asticky mass formed, and its X-ray diffraction diagram showed only thediffraction lines of quartz (FIG. 2 ).

We claim:
 1. A process for the production of crystalline sodium sheetsilicate having kanemite structure and having the chemical formula

    NaH Si.sub.2 O.sub.5 ·XH.sub.2 O

in which X represents a value between 1 and 3, which comprises mixingδ-Na₂ Si₂ O₅, or a mixture of δ-Na₂ Si₂ O₅ and up to 80% by weight ofamorphous Na₂ Si₂ O₅ ·nH₂ O, with silica and water in a molar ratio of1:2:(6-8) and maintaining the mixture at a temperature of 20° to 100° C.for a period of 0.2 to 10 h to produce said crystalline sodium sheetsilicate having kanemite structure.
 2. The process as claimed in claim1, wherein precipitated silica, pyrogenic silica, silica sol or silicagel is employed as silica.
 3. The process as claimed in claim 1, whereinthe sodium disilicate is employed with a particle fineness of less than1000 μm.
 4. The process as claimed in claim 1, wherein the silica isemployed with a particle fineness of less than 200 μm.
 5. The process asclaimed in claim 1, wherein the reaction product is maintained at 50° to100° C. for a further 0.5 to 5 h.
 6. The process as claimed in claim 1,wherein the crystalline sodium sheet silicate with kanemite structure iscomminuted by milling to a particle fineness of less than 100 μm.